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Naming of parts - cams and valvetrain

Posted: June 26th, 2006, 10:10 am
by Guy Croft
1. The 'top hat' shim or 'lash cap is often used to take up the clearance that is created when changing from standard cams to competition cam. Competition cams often have a smaller diameter base-circle. Top hats just sit on the valve tip with a good, but not necessarily tight fit. Best material is alloy steel like En36 which contains nickel and case-hardens well to say 15 thou deep, allowing for finish grinding, and thus resists wear without becoming too brittle.
Top-hats must not bear against the collets or the fretting will severly damage the valves and spring caps. Fitting requires great care - always do a dry run without them and take measurements then fit them and re-measure. If the clearances are not reduced by the thickness of the top-hat, one has become dislodged.

2.Identifying the different sections of the camshaft. This is a Fiat 8v TC cam, where there are no separate bearings, the cam runs direct in the housing.